Electrical lighting fixtures of the metal halide, mercury vapor and high pressure sodium types employ ballast transformers to provide appropriate electrical voltages and currents to energize the lamp or lamps mounted in the fixture. The enclosures or housings used in these fixtures may be composed wholly or partially of a polymeric material because of its relatively light weight and ease of moldability into esthetic designs.
The ballast is formed of a stack of flat laminations of magnetizable iron which are cut out in various shapes to receive one or more electrical coils. The ballast laminations are held together by screws or bolts which pass perpendicularly through the laminations adjacent each corner thereof. By virtue of their high metallic content, each ballast may weigh two or more pounds and if the fixture is largely composed of a polymeric material, there exists the possibility that the ballast is being retained on a polymeric supporting surface.
For lighting fixtures having housings comprised of polymeric materials, the Mar. 26, 1980 Underwriters Laboratory Code entitled "High Intensity Discharge Lighting Fixtures--UL 1572" under Subsection 54.1 thereof is relevant in its requirement that "A polymeric material, thermoplastic or thermosetting, used to provide all or any part of the enclosure for electrical parts . . . that provides structural support in a fixture, shall comply with the requirements of this section.".
The additional pertinent requirement is stated in Subsection 54.9 as follows: "Any nonpolymeric part that weighs more than 2 pounds (0.91 kg) shall be connected to the mounting means of the fixture by a metal chain, cable or equivalent.". A "nonpolymeric part" which falls within this definition would include a ballast.
A principal reason behind these requirements is that the mounting of the ballast to a polymeric part of the housing may create a hazardous situation if that part of the fixture is consumed by fire. In such case, the polymeric ballast might be released to fall freely from the fixture. As will be evident, a possible safety problem to firefighters can be created by ballasts falling from ceiling or wall mounted fixtures.
To prevent the ballast from falling from these types of fixtures in a fire situation, Underwriters Laboratory has, in effect, mandated that the ballast be connected to the fixture mounting means (which is typically the metal bridge or "hickey" of an electrical outlet box) by a "metal chain, cable or equivalent". As may be appreciated, the manual connection of chains and cables to the fixture mounting by the luminaire installer, who is typically an electrician, can, however, prove troublesome, time-consuming and in some cases, omitted deliberately or through oversight.